The improvements of our invention are adapted to be used in electro-hydraulic control systems for estimating pressure in a hydraulic pressure actuator. Our pressure estimation method is adaptable, for example, for use in obtaining a brake pressure signal at the wheel brake actuators of an automotive wheel brake system having anti-lock braking capabilities. It also is adaptable for use in the wheel brake system for effecting anti-wheel spin control and interactive vehicle dynamics control.
In the case of a brake system having antiwheel spin capabilities, a loss of traction can be avoided when the road surface friction changes wheel traction. Vehicle handling capabilities can be ensured as the electronically controlled brakes quickly contain wheel spin independent of driver intervention.
In the case of anti-lock brake systems, the source of pressure is the brake master cylinder. In this implementation, there are two on/off solenoids for controlling each wheel brake pressure actuator, one controlling the brake pressure fill and the other controlling the brake pressure dump. Brake pressure is increased by the normally-open fill solenoids and brake pressure is decreased by the normally-closed exhaust solenoids, which vent the brake pressure to the reservoir.
An important feature of control systems of this kind is the ability to use brake pressure as input information for an electronic controller. The wheel brake pressure must be known in order to achieve the desired control of the interactive vehicle dynamics such as brake-controlled steering. The most direct way to obtain this information is by using pressure transducers. In practice, however, it is not feasible to use pressure transducers in the harsh environment of a vehicle wheel brake. Although a durable and reliable pressure transducer could be used in such environments, the variable cost of manufacturing a brake system with such a pressure transducer would be significantly increased.